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class="post-meta-label">字数总计:</span><span class="word-count">2.1k</span><span class="post-meta-separator">|</span><i class="far fa-clock fa-fw post-meta-icon"></i><span class="post-meta-label">阅读时长:</span><span>8分钟</span></span><span class="post-meta-separator">|</span><span class="post-meta-pv-cv" id="" data-flag-title="JavaWeb🌍EL表达式"><i class="far fa-eye fa-fw post-meta-icon"></i><span class="post-meta-label">阅读量:</span><span id="busuanzi_value_page_pv"></span></span></div></div></div><article class="post-content" id="article-container"><h1 id="EL表达式"><a href="#EL表达式" class="headerlink" title="EL表达式"></a>EL表达式</h1><ul>
<li>EL：Expression Language，一种简单的数据访问语言，可以在JSP页面中直接使用！ </li>
<li>是一种在JSP页面获取数据的简单方式（只能获取数据，不能设置数据）</li>
<li>在JSP页面的任何静态部分均可通过：<code>$&#123;expression&#125;</code>来获取到指定表达式的值</li>
<li>需要导入jar包</li>
</ul>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">dependency</span>&gt;</span></span><br><span class="line">   <span class="tag">&lt;<span class="name">groupId</span>&gt;</span>javax.servlet.jsp.jstl<span class="tag">&lt;/<span class="name">groupId</span>&gt;</span></span><br><span class="line">   <span class="tag">&lt;<span class="name">artifactId</span>&gt;</span>jstl<span class="tag">&lt;/<span class="name">artifactId</span>&gt;</span></span><br><span class="line">   <span class="tag">&lt;<span class="name">version</span>&gt;</span>1.2<span class="tag">&lt;/<span class="name">version</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">dependency</span>&gt;</span></span><br></pre></td></tr></table></figure>

<ul>
<li>如果出现EL表达式无效，需要在JSP页面引入如下语句</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">isELIgnored</span>=<span class="string">&quot;false&quot;</span>%&gt;</span></span><br></pre></td></tr></table></figure>

<h2 id="EL简单实例"><a href="#EL简单实例" class="headerlink" title="EL简单实例"></a>EL简单实例</h2><ul>
<li>定义一个<code>MyServlet</code>设置<code>username</code>和<code>password</code>参数的值，然后请求转发到<code>myjsp.jsp</code>页面，通过<code>EL</code>表达式取值</li>
</ul>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyServlet</span> <span class="keyword">extends</span> <span class="title">HttpServlet</span> </span>&#123;</span><br><span class="line">   <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">doGet</span><span class="params">(HttpServletRequest request, HttpServletResponse  response)</span> <span class="keyword">throws</span> ServletException, IOException </span>&#123;</span><br><span class="line">      request.setAttribute(<span class="string">&quot;username&quot;</span>, <span class="string">&quot;itcast&quot;</span>);</span><br><span class="line">      request.setAttribute(<span class="string">&quot;password&quot;</span>, <span class="string">&quot;123&quot;</span>);</span><br><span class="line">      RequestDispatcher dispatcher = request.getRequestDispatcher(<span class="string">&quot;/myjsp.jsp&quot;</span>);</span><br><span class="line">      dispatcher.forward(request, response);</span><br><span class="line">   &#125;</span><br></pre></td></tr></table></figure>

<ul>
<li><code>myjsp.jsp</code>页面用于取值</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">language</span>=<span class="string">&quot;java&quot;</span> <span class="attr">contentType</span>=<span class="string">&quot;text/html; charset=utf-8&quot;</span></span></span><br><span class="line"><span class="tag">	<span class="attr">pageEncoding</span>=<span class="string">&quot;utf-8&quot;</span>%&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">head</span>&gt;</span><span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">   使用JSP表达式:<span class="tag">&lt;<span class="name">br</span>/&gt;</span></span><br><span class="line">   用户名：<span class="tag">&lt;<span class="name">%=request.getAttribute(&quot;username&quot;)%</span>&gt;</span><span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">   密 码：<span class="tag">&lt;<span class="name">%=request.getAttribute(&quot;password&quot;)%</span>&gt;</span><span class="tag">&lt;<span class="name">br</span> /&gt;</span>	</span><br><span class="line">   <span class="tag">&lt;<span class="name">hr</span>&gt;</span></span><br><span class="line">   使用EL表达式:<span class="tag">&lt;<span class="name">br</span> /&gt;</span></span><br><span class="line">   用户名：$&#123;username&#125;<span class="tag">&lt;<span class="name">br</span> /&gt;</span></span><br><span class="line">   密 码：$&#123;password&#125;<span class="tag">&lt;<span class="name">br</span> /&gt;</span></span><br><span class="line">   </span><br><span class="line"><span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
<h2 id="EL标识符"><a href="#EL标识符" class="headerlink" title="EL标识符"></a>EL标识符</h2><ul>
<li>不能以数字开头</li>
<li>不能是EL中的保留字，如and、or、gt</li>
<li>不能是EL隐式对象，如pageContext</li>
<li>不能包含单引号（’）、双引号（”）、减号（-）和正斜线等特殊字符。</li>
<li>保留字就是编程语言里事先定义好并赋予了特殊含义的单词，和其他语言一样，EL表达式中也定义了许多保留字，如false、not等，接下来就列举EL中所有的保留字，具体如下：</li>
</ul>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">and	     eq	       gt	       <span class="keyword">true</span>	       <span class="keyword">instanceof</span>	</span><br><span class="line">or	     ne	       le	       <span class="keyword">false</span>	       empty	</span><br><span class="line">not	     lt	       ge	       <span class="keyword">null</span>	       div	       mod</span><br></pre></td></tr></table></figure>
<h2 id="EL变量常量"><a href="#EL变量常量" class="headerlink" title="EL变量常量"></a>EL变量常量</h2><ul>
<li>EL表达式中的变量就是一个基本的存储单元，EL表达式可以将变量映射到一个对象上，具体示例如下所示：</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$&#123;product&#125;</span><br></pre></td></tr></table></figure>

<div class="note success simple"><p>product就是一个变量。EL表达式中的变量不用事先定义就可以直接使用，例如，表达式<code>${product}</code>就可以访问变量product的值。</p>
</div>

<table>
<thead>
<tr>
<th align="center">EL常量</th>
<th align="center">说明</th>
</tr>
</thead>
<tbody><tr>
<td align="center">布尔常量</td>
<td align="center">true和false</td>
</tr>
<tr>
<td align="center">整型常量</td>
<td align="center">（-2）63~263-1之间的整数</td>
</tr>
<tr>
<td align="center">浮点型常量</td>
<td align="center">4.9E-324~1.8E308之间的整数</td>
</tr>
<tr>
<td align="center">字符串常量</td>
<td align="center">用单引号或双引号引起来的一连串字符</td>
</tr>
<tr>
<td align="center">Null常量</td>
<td align="center">用于表示变量引用的对象为空，它只有一个值，用null表示</td>
</tr>
</tbody></table>
<h2 id="EL运算符"><a href="#EL运算符" class="headerlink" title="EL运算符"></a>EL运算符</h2><ul>
<li>EL表达式支持简单的运算，例如，加（+）、减（-）、乘（*）、除（/）等。为此，在EL中提供了多种运算符，EL中的运算符包括以下几种：</li>
</ul>
<img src="https://cdn.jsdelivr.net/gh/lzyblog/image@main/2020/12/26/32cf12aa081a463db629c99562084317.png" width="60%">

<table>
<thead>
<tr>
<th align="center">运算符</th>
<th align="center">说明</th>
<th align="center">实例</th>
</tr>
</thead>
<tbody><tr>
<td align="center">点运算符<code>.</code></td>
<td align="center">访问某些对象的属性</td>
<td align="center">${people.name}</td>
</tr>
<tr>
<td align="center">方括号运算符<code>[ ]</code></td>
<td align="center">与点运算符类似，应用于属性名中包含一些特殊符号时取值</td>
<td align="center">${user[“My-Name”]}</td>
</tr>
<tr>
<td align="center">算术运算符</td>
<td align="center">+、-、*、/、%</td>
<td align="center"></td>
</tr>
<tr>
<td align="center">比较运算符</td>
<td align="center">结果为布尔类型，==、！=、&lt;、&gt;、&lt;=、&gt;=</td>
<td align="center"></td>
</tr>
<tr>
<td align="center">逻辑运算符</td>
<td align="center">结果为布尔类型，&amp;&amp;、</td>
<td align="center"></td>
</tr>
<tr>
<td align="center">empty运算符</td>
<td align="center">判断某个对象是否为null或” ”，结果为布尔类型</td>
<td align="center">${empty var}</td>
</tr>
<tr>
<td align="center">条件运算符</td>
<td align="center">类似于Java语言中的if-else语句</td>
<td align="center">${A?B:C}</td>
</tr>
<tr>
<td align="center"><code>()</code>运算符</td>
<td align="center">EL表达式中的圆括号用于改变其它运算符的优先级</td>
<td align="center"></td>
</tr>
</tbody></table>
<h1 id="EL隐式对象"><a href="#EL隐式对象" class="headerlink" title="EL隐式对象"></a>EL隐式对象</h1><ul>
<li>EL中<code>11个</code>隐式对象</li>
</ul>
<p><img src="https://cdn.jsdelivr.net/gh/lzyblog/image@main/2020/12/26/ffb7cfe9c7c742da8dccb092d649777b.png"></p>
<h2 id="pageContext对象"><a href="#pageContext对象" class="headerlink" title="pageContext对象"></a>pageContext对象</h2><ul>
<li>为了获取JSP页面的隐式对象，可以使用EL表达式中的pageContext隐式对象获取其他10个隐式对象。 pageContext隐式对象的示例代码如下：</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$&#123;pageContext.response.characterEncoding&#125;</span><br></pre></td></tr></table></figure>

<ul>
<li>pageContext对象获取response对象中的characterEncoding属性</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">language</span>=<span class="string">&quot;java&quot;</span> <span class="attr">contentType</span>=<span class="string">&quot;text/html; charset=utf-8&quot;</span></span></span><br><span class="line"><span class="tag">	<span class="attr">pageEncoding</span>=<span class="string">&quot;utf-8&quot;</span>%&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">head</span>&gt;</span><span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">   请求URI为：$&#123;pageContext.request.requestURI&#125; <span class="tag">&lt;<span class="name">br</span> /&gt;</span></span><br><span class="line">   Content-Type响应头：$&#123;pageContext.response.contentType&#125; <span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">   服务器信息为：$&#123;pageContext.servletContext.serverInfo&#125; <span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">   Servlet注册名为：$&#123;pageContext.servletConfig.servletName&#125; <span class="tag">&lt;<span class="name">br</span> /&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>

<p><img src="https://cdn.jsdelivr.net/gh/lzyblog/image@main/2020/12/26/08bedc07bcad2569d6f05a4b5dd60f81.png"></p>
<h2 id="Web域相关对象"><a href="#Web域相关对象" class="headerlink" title="Web域相关对象"></a>Web域相关对象</h2><ul>
<li>HttpRequest对象存储的数据只在当前请求中可以获取到。习惯性的，我们把这些Map集合称为域，这些Map集合所在的对象称为域对象。在EL表达式中，为了获取指定域中的数据，提供了<code>pageScope</code>、<code>requestScope</code>、<code>sessionScope</code>和<code>applicationScope</code>(<strong>范围由小到大</strong>)四个隐式对象，示例代码如下</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">$&#123;pageScope.userName&#125; 		$&#123;requestScope.userName&#125; </span><br><span class="line">$&#123;sessionScope.userName&#125; 	$&#123;applicationScope.userName&#125;</span><br></pre></td></tr></table></figure>

<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">language</span>=<span class="string">&quot;java&quot;</span> <span class="attr">contentType</span>=<span class="string">&quot;text/html; charset=utf-8&quot;</span></span></span><br><span class="line"><span class="tag">	<span class="attr">pageEncoding</span>=<span class="string">&quot;utf-8&quot;</span>%&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">head</span>&gt;</span><span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">   <span class="tag">&lt;<span class="name">%</span> <span class="attr">pageContext.setAttribute</span>(&quot;<span class="attr">userName</span>&quot;, &quot;<span class="attr">itcast</span>&quot;); %&gt;</span></span><br><span class="line">   <span class="tag">&lt;<span class="name">%</span> <span class="attr">request.setAttribute</span>(&quot;<span class="attr">bookName</span>&quot;, &quot;<span class="attr">Java</span> <span class="attr">Web</span>&quot;); %&gt;</span></span><br><span class="line">   <span class="tag">&lt;<span class="name">%</span> <span class="attr">session.setAttribute</span>(&quot;<span class="attr">userName</span>&quot;, &quot;<span class="attr">itheima</span>&quot;); %&gt;</span></span><br><span class="line">   <span class="tag">&lt;<span class="name">%</span> <span class="attr">application.setAttribute</span>(&quot;<span class="attr">bookName</span>&quot;, &quot;<span class="attr">Java</span> 基础&quot;); %&gt;</span></span><br><span class="line">   表达式\$&#123;pageScope.userName&#125;的值为：$&#123;pageScope.userName&#125; <span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">   表达式\$&#123;requestScope.bookName&#125;的值为：$&#123;requestScope.bookName&#125; <span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">   表达式\$&#123;sessionScope.userName&#125;的值为：$&#123;sessionScope.userName&#125; <span class="tag">&lt;<span class="name">br</span> /&gt;</span></span><br><span class="line">   表达式\$&#123;applicationScope.bookName&#125;的值为：$&#123;applicationScope.bookName&#125; </span><br><span class="line">   <span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">   表达式\$&#123;userName&#125;的值为：$&#123;userName&#125;</span><br><span class="line"><span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
<p><img src="https://cdn.jsdelivr.net/gh/lzyblog/image@main/2020/12/26/d5af5f595332d313c549e8a317ad962a.png"></p>
<h2 id="param和paramValues对象"><a href="#param和paramValues对象" class="headerlink" title="param和paramValues对象"></a>param和paramValues对象</h2><ul>
<li>param对象用于获取请求参数的某个值，它是Map类型，与request.getParameter()方法相同，在使用EL获取参数时，如果参数不存在，返回的是空字符串，而不是null，具体示例如下：</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$&#123;param.num&#125;</span><br></pre></td></tr></table></figure>

<ul>
<li>如果一个请求参数有多个值，可以使用paramValues对象来获取请求参数的所有值，该对象用于返回请求参数所有值组成的数组，如果要获取某个请求参数的第一个值，可以使用如下代码：</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$&#123;paramValues.nums[0]&#125; </span><br></pre></td></tr></table></figure>

<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">language</span>=<span class="string">&quot;java&quot;</span> <span class="attr">contentType</span>=<span class="string">&quot;text/html; charset=utf-8&quot;</span></span></span><br><span class="line"><span class="tag">	<span class="attr">pageEncoding</span>=<span class="string">&quot;utf-8&quot;</span>%&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">head</span>&gt;</span><span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">body</span> <span class="attr">style</span>=<span class="string">&quot;text-align: center;&quot;</span>&gt;</span></span><br><span class="line">   <span class="tag">&lt;<span class="name">form</span> <span class="attr">action</span>=<span class="string">&quot;$&#123;pageContext.request.contextPath&#125;/param.jsp&quot;</span>&gt;</span></span><br><span class="line">      num1：<span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">&quot;text&quot;</span> <span class="attr">name</span>=<span class="string">&quot;num1&quot;</span>&gt;</span><span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">      num2：<span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">&quot;text&quot;</span> <span class="attr">name</span>=<span class="string">&quot;num&quot;</span>&gt;</span><span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">      num3：<span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">&quot;text&quot;</span> <span class="attr">name</span>=<span class="string">&quot;num&quot;</span>&gt;</span><span class="tag">&lt;<span class="name">br</span> /&gt;</span> <span class="tag">&lt;<span class="name">br</span> /&gt;</span></span><br><span class="line">      <span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">&quot;submit&quot;</span> <span class="attr">value</span>=<span class="string">&quot;提交&quot;</span> /&gt;</span><span class="symbol">&amp;nbsp;</span><span class="symbol">&amp;nbsp;</span></span><br><span class="line">      <span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">&quot;submit&quot;</span> <span class="attr">value</span>=<span class="string">&quot;重置&quot;</span> /&gt;</span></span><br><span class="line">      <span class="tag">&lt;<span class="name">hr</span>&gt;</span></span><br><span class="line">      num1：$&#123;param.num1&#125;<span class="tag">&lt;<span class="name">br</span> /&gt;</span></span><br><span class="line">      num2：$&#123;paramValues.num[0]&#125;<span class="tag">&lt;<span class="name">br</span> /&gt;</span></span><br><span class="line">      num3：$&#123;paramValues.num[1]&#125;<span class="tag">&lt;<span class="name">br</span> /&gt;</span></span><br><span class="line">   <span class="tag">&lt;/<span class="name">form</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
<p><img src="https://cdn.jsdelivr.net/gh/lzyblog/image@main/2020/12/26/84d9c560b5e429d9003816d64990731d.png"></p>
<h2 id="header和headerValues对象"><a href="#header和headerValues对象" class="headerlink" title="header和headerValues对象"></a>header和headerValues对象</h2><ul>
<li> header对象用于获取请求头字段的某个值，具体示例如下：</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$&#123;header[&quot;user-agent&quot;]&#125;</span><br></pre></td></tr></table></figure>

<ul>
<li>如果一个请求头字段有多个值，可以使用headerValues对象，该对象用于返回请求头字符的所有值组成的数组，如果要获取某个请求头字段的第一个值，可以使用如下代码： </li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$&#123;headerValues[&quot;Accept-Language&quot;][0]&#125;</span><br></pre></td></tr></table></figure>

<h2 id="Cookie对象"><a href="#Cookie对象" class="headerlink" title="Cookie对象"></a>Cookie对象</h2><ul>
<li>在JSP开发中，经常需要获取客户端的Cookie信息，为此，在EL表达式中，提供了Cookie隐式对象，该对象是一个代表所有Cookie信息的Map集合， Map集合中元素的关键字为各个Cookie的名称，值则为对应的Cookie对象，具体示例如下：</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">获取cookie对象的信息：$&#123;cookie.userName&#125;</span><br><span class="line">获取cookie对象的名称：$&#123;cookie.userName.name&#125;</span><br><span class="line">获取cookie对象的值：$&#123;cookie.userName.value&#125;</span><br></pre></td></tr></table></figure>

<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">language</span>=<span class="string">&quot;java&quot;</span> <span class="attr">contentType</span>=<span class="string">&quot;text/html; charset=utf-8&quot;</span></span></span><br><span class="line"><span class="tag">	<span class="attr">pageEncoding</span>=<span class="string">&quot;utf-8&quot;</span>%&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">head</span>&gt;</span><span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">   Cookie对象的信息：<span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">   $&#123;cookie.userName &#125; <span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">   Cookie对象的名称和值：<span class="tag">&lt;<span class="name">br</span> /&gt;</span> </span><br><span class="line">   $&#123;cookie.userName.name &#125;=$&#123;cookie.userName.value &#125;</span><br><span class="line">	<span class="tag">&lt;<span class="name">%</span> <span class="attr">response.addCookie</span>(<span class="attr">new</span> <span class="attr">Cookie</span>(&quot;<span class="attr">userName</span>&quot;, &quot;<span class="attr">itcast</span>&quot;)); %&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
<p><img src="https://cdn.jsdelivr.net/gh/lzyblog/image@main/2020/12/26/2129243477c2df72040944e8b01922bc.png"></p>
<ul>
<li>第一次访问并不会显示信息，服务器会向浏览器回写一个Cookie，此时的Cookie信息存储在浏览器中，当刷新页面第二次访问时，浏览器会将此Cookie信息一同发送给服务器，使用表达式获取名称和值</li>
</ul>
<h2 id="initParam对象"><a href="#initParam对象" class="headerlink" title="initParam对象"></a>initParam对象</h2><ul>
<li>在开发一个Web应用程序时，通常会在web.xml文件中配置一些初始化参数，为了方便获取这些参数，EL表达式提供了一个initParam隐式对象，该对象可以获取Web应用程序中全局初始化参数，具体示例如下所示：</li>
</ul>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$&#123;initParam.count&#125; </span><br></pre></td></tr></table></figure></article><div class="post-copyright"><div class="post-copyright__author"><span class="post-copyright-meta">文章作者: </span><span class="post-copyright-info"><a href="mailto:undefined">小李博客</a></span></div><div class="post-copyright__type"><span class="post-copyright-meta">文章链接: </span><span class="post-copyright-info"><a href="https://xiaoliblog.cn">https://xiaoliblog.cn</a></span></div><div class="post-copyright__notice"><span class="post-copyright-meta">版权声明: </span><span class="post-copyright-info">本博客所有文章除特别声明外，均采用 <a href="https://creativecommons.org/licenses/by-nc-sa/4.0/" target="_blank">CC BY-NC-SA 4.0</a> 许可协议。转载请注明来自 <a href="http://xiaoliblog.cn" target="_blank">小李博客</a>！</span></div></div><div class="tag_share"><div class="post-meta__tag-list"><a 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class="toc-text">EL变量常量</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#EL%E8%BF%90%E7%AE%97%E7%AC%A6"><span class="toc-number">1.4.</span> <span class="toc-text">EL运算符</span></a></li></ol></li><li class="toc-item toc-level-1"><a class="toc-link" href="#EL%E9%9A%90%E5%BC%8F%E5%AF%B9%E8%B1%A1"><span class="toc-number">2.</span> <span class="toc-text">EL隐式对象</span></a><ol class="toc-child"><li class="toc-item toc-level-2"><a class="toc-link" href="#pageContext%E5%AF%B9%E8%B1%A1"><span class="toc-number">2.1.</span> <span class="toc-text">pageContext对象</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#Web%E5%9F%9F%E7%9B%B8%E5%85%B3%E5%AF%B9%E8%B1%A1"><span class="toc-number">2.2.</span> <span class="toc-text">Web域相关对象</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#param%E5%92%8CparamValues%E5%AF%B9%E8%B1%A1"><span class="toc-number">2.3.</span> <span class="toc-text">param和paramValues对象</span></a></li><li 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    getScript('https://cdn.jsdelivr.net/npm/mermaid/dist/mermaid.min.js').then(() => {
      window.mermaidJsLoad = true
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}</script><script>(()=>{
  const $countDom = document.getElementById('twikoo-count')
  const init = () => {
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      el: '#twikoo-wrap',
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  const getCount = () => {
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  const loadTwikoo = (bool = false) => {
    if (typeof twikoo === 'object') {
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      bool && $countDom && setTimeout(getCount,0)
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      getScript('https://cdn.jsdelivr.net/npm/twikoo@1.3.0/dist/twikoo.all.min.js').then(()=> {
        init()
        bool && $countDom && setTimeout(getCount,0)
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  }

  if ('Twikoo' === 'Twikoo' || !true) {
    if (true) btf.loadComment(document.getElementById('twikoo-wrap'), loadTwikoo)
    else loadTwikoo(true)
  } else {
    window.loadOtherComment = () => {
      loadTwikoo()
    }
  }
})()</script></div><script defer src="//lib.baomitu.com/jquery/3.5.1/jquery.min.js"></script><script defer src="https://myhkw.cn/api/player/160561664166" id="myhk" key="160561664166" m="1"></script><div><canvas id="snow" style="position:fixed;top:0;left:0;width:100%;height:100%;z-index:99999;pointer-events:none"></canvas></div><script>const notMobile = (!(navigator.userAgent.match(/(phone|pad|pod|iPhone|iPod|ios|iPad|Android|Mobile|BlackBerry|IEMobile|MQQBrowser|JUC|Fennec|wOSBrowser|BrowserNG|WebOS|Symbian|Windows Phone)/i)));</script><scrip async type="text/javascript" src="https://cdn.jsdelivr.net/gh/Candinya/Kratos-Rebirth@latest/source/js/snow.min.js"></scrip><scrip defer src="https://cdn.jsdelivr.net/npm/hexo-theme-volantis@latest/source/js/issues.min.js"></scrip><script async data-pjax src="//busuanzi.ibruce.info/busuanzi/2.3/busuanzi.pure.mini.js"></script><script>var gitcalendar = new Vue({
  el: '#gitcalendar',
  data: {
    simplemode: true, 
    user: 'xiaoliblog',
    fixed: 'fixed',
    px: 'px',
    x: '',
    y: '',
    span1: '',
    span2: '',
    month: ['一月', '二月', '三月', '四月', '五月', '六月', '七月', '八月', '九月', '十月', '十一月', '十二月'],
    monthchange: [],
    oneyearbeforeday: '',
    thisday: '',
    amonthago: '',
    aweekago: '',
    weekdatacore: 0,
    datacore: 0,
    total: 0,
    datadate: '',
    data: [],
    positionplusdata: [],
    firstweek: [],
    lastweek: [],
    beforeweek: [],
    thisweekdatacore: 0,
    mounthbeforeday: 0,
    mounthfirstindex: 0,
    crispedges: 'crispedges',
    thisdayindex: 0,
    amonthagoindex: 0,
    amonthagoweek: [],
    firstdate: [],
    first2date: [],
    montharrbefore: [],
    monthindex: 0,
    color: ['#ebedf0', '#f1f8ff', '#dbedff', '#c8e1ff', '#79b8ff', '#2188ff', '#0366d6', '#005cc5', '#044289', '#032f62', '#05264c']
  },
  methods: {
    selectStyle(data, event) {
      document.querySelector('.angle-wrapper').style.display = 'block'
      this.span1 = data.date;
      this.span2 = data.count;
      this.x = event.clientX - 100;
      this.y = event.clientY - 60
    },
    outStyle() {
      document.querySelector('.angle-wrapper').style.display = 'none'
    },
    thiscolor(x) {
      if (x === 0) {
        let i = parseInt(x / 2);
        return this.color[0]
      } else if (x < 2) {
        return this.color[1]
      } else if (x < 20) {
        let i = parseInt(x / 2);
        return this.color[i]
      } else {
        return this.color[9]
      }
    },
  }
});
var apiurl = 'python-github-calendar-api-ruby.vercel.app' ? 'https://python-github-calendar-api-ruby.vercel.app/api?' : 'https://githubapi.ryanchristian.dev/user/'
var githubapiurl = apiurl + gitcalendar.user;
//canvas绘图
function responsiveChart() {
  let c = document.getElementById("gitcanvas");
  if (c) {
    let cmessage = document.getElementById("gitmessage");
    let ctx = c.getContext("2d");
    c.width = document.getElementById("gitcalendarcanvasbox").offsetWidth;
    let linemaxwitdh = 0.96 * c.width / gitcalendar.data.length;
    c.height = 9 * linemaxwitdh;
    let lineminwitdh = 0.8 * linemaxwitdh;
    let setposition = {
      x: 0.02 * c.width,
      y: 0.025 * c.width
    };
    for (let week in gitcalendar.data) {
      weekdata = gitcalendar.data[week];
      for (let day in weekdata) {
        let dataitem = {
          date: "",
          count: "",
          x: 0,
          y: 0
        };
        gitcalendar.positionplusdata.push(dataitem);
        ctx.fillStyle = gitcalendar.thiscolor(weekdata[day].count);
        setposition.y = Math.round(setposition.y * 100) / 100;
        dataitem.date = weekdata[day].date;
        dataitem.count = weekdata[day].count;
        dataitem.x = setposition.x;
        dataitem.y = setposition.y;
        ctx.fillRect(setposition.x, setposition.y, lineminwitdh, lineminwitdh);
        setposition.y = setposition.y + linemaxwitdh
      };
      setposition.y = 0.025 * c.width;
      setposition.x = setposition.x + linemaxwitdh
    };
    ctx.font = "600  Arial";
    ctx.fillStyle = '#aaa';
    ctx.fillText("日", 0, 1.9 * linemaxwitdh);
    ctx.fillText("二", 0, 3.9 * linemaxwitdh);
    ctx.fillText("四", 0, 5.9 * linemaxwitdh);
    ctx.fillText("六", 0, 7.9 * linemaxwitdh);
    let monthindexlist = c.width / 24;
    for (let index in gitcalendar.monthchange) {
      ctx.fillText(gitcalendar.monthchange[index], monthindexlist, 0.7 * linemaxwitdh);
      monthindexlist = monthindexlist + c.width / 12
    };
    cmessage.onmousemove = function(event) {
      document.querySelector('.angle-wrapper').style.display = 'none'
    };
    c.onmousemove = function(event) {
      document.querySelector('.angle-wrapper').style.display = 'none'
      getMousePos(c, event);
    };

    function getMousePos(canvas, event) {
      var rect = canvas.getBoundingClientRect();
      var x = event.clientX - rect.left * (canvas.width / rect.width);
      var y = event.clientY - rect.top * (canvas.height / rect.height);
      //console.log("x:"+x+",y:"+y);
      for (let item of gitcalendar.positionplusdata) {
        let lenthx = x - item.x;
        let lenthy = y - item.y;
        //console.log(lenthx,lenthy);
        if (0 < lenthx && lenthx < lineminwitdh) {
          if (0 < lenthy && lenthy < lineminwitdh) {
            //console.log(item.date,item.count)
            document.querySelector('.angle-wrapper').style.display = 'block'
            gitcalendar.span1 = item.date;
            gitcalendar.span2 = item.count;
            gitcalendar.x = event.clientX - 100;
            gitcalendar.y = event.clientY - 60
          }
        }
        //if(0< x - item.x <lineminwitdh&&0< y - item.y <lineminwitdh){
        //console.log(item.count,item.date);
        //}
      }
    }
  }
}
//数据统计算法
function addlastmonth() {
  if (gitcalendar.thisdayindex === 0) {
    thisweekcore(52);
    thisweekcore(51);
    thisweekcore(50);
    thisweekcore(49);
    thisweekcore(48);
    gitcalendar.thisweekdatacore += gitcalendar.firstdate[6].count;
    gitcalendar.amonthago = gitcalendar.firstdate[6].date
  } else {
    thisweekcore(52);
    thisweekcore(51);
    thisweekcore(50);
    thisweekcore(49);
    thisweek2core();
    gitcalendar.amonthago = gitcalendar.first2date[gitcalendar.thisdayindex - 1].date
  }
};

function thisweek2core() {
  for (let i = gitcalendar.thisdayindex - 1; i < gitcalendar.first2date.length; i++) {
    gitcalendar.thisweekdatacore += gitcalendar.first2date[i].count
  }
};

function thisweekcore(index) {
  for (let item of gitcalendar.data[index]) {
    gitcalendar.thisweekdatacore += item.count
  }
};

function addlastweek() {
  for (let item of gitcalendar.lastweek) {
    gitcalendar.weekdatacore += item.count
  }
};

function addbeforeweek() {
  for (let i = gitcalendar.thisdayindex; i < gitcalendar.beforeweek.length; i++) {
    gitcalendar.weekdatacore += gitcalendar.beforeweek[i].count
  }
};

function addweek(data) {
  if (gitcalendar.thisdayindex === 6) {
    gitcalendar.aweekago = gitcalendar.lastweek[0].date;
    addlastweek()
  } else {
    lastweek = data.contributions[51];
    gitcalendar.aweekago = lastweek[gitcalendar.thisdayindex + 1].date;
    addlastweek();
    addbeforeweek()
  }
}

fetch(githubapiurl)
  .then(data => data.json())
  .then(data => {
    gitcalendar.data = data.contributions;
    gitcalendar.total = data.total;
    gitcalendar.first2date = gitcalendar.data[48];
    gitcalendar.firstdate = gitcalendar.data[47];
    gitcalendar.firstweek = data.contributions[0];
    gitcalendar.lastweek = data.contributions[52];
    gitcalendar.beforeweek = data.contributions[51];
    gitcalendar.thisdayindex = gitcalendar.lastweek.length - 1;
    gitcalendar.thisday = gitcalendar.lastweek[gitcalendar.thisdayindex].date;
    gitcalendar.oneyearbeforeday = gitcalendar.firstweek[0].date;
    gitcalendar.monthindex = gitcalendar.thisday.substring(5, 7) * 1;
    gitcalendar.montharrbefore = gitcalendar.month.splice(gitcalendar.monthindex, 12 - gitcalendar.monthindex);
    gitcalendar.monthchange = gitcalendar.montharrbefore.concat(gitcalendar.month);
    addweek(data);
    addlastmonth();
    responsiveChart();
  })
  .catch(function(error) {
    console.log(error);
  });

//手机版更换为svg绘制
if (document.getElementById("gitcalendarcanvasbox").offsetWidth < 500) {
  gitcalendar.simplemode = false
}

//当改变窗口大小时重新绘制canvas
window.onresize = function() {
  if (gitcalendar.simplemode) responsiveChart()
}

//解决滚动滑轮时出现的标签显示
window.onscroll = function() {
  if (document.querySelector('.angle-wrapper')) {
    document.querySelector('.angle-wrapper').style.display = 'none'
  }
};</script></div><script src="/live2dw/lib/L2Dwidget.min.js?094cbace49a39548bed64abff5988b05"></script><script>L2Dwidget.init({"pluginRootPath":"live2dw/","pluginJsPath":"lib/","pluginModelPath":"assets/","tagMode":false,"log":false,"model":{"jsonPath":"/live2dw/assets/hijiki.model.json"},"display":{"position":"right","width":150,"height":300},"mobile":{"show":true},"react":{"opacity":0.7}});</script></body></html>